Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
FIG. 1 shows a conventional bump structure formed over semiconductor wafer 10 containing a base substrate material such as silicon, germanium, gallium arsenide, indium phosphide, or silicon carbide, for structural support. A plurality of semiconductor die is formed on semiconductor wafer 10. Each semiconductor die has an active surface 12 containing analog or digital circuits implemented as active devices, passive devices, conductive layers, and dielectric layers formed within the die and electrically interconnected according to the electrical design and function of the die. Metal interconnect pads 14 are formed over active surface 12. Metal pads 14 are electrically connected to circuitry on active surface 12. A passivation layer 16 is formed over active surface 12 and metal pads 14. A portion of passivation layer 16 is removed by an etching process to expose metal pads 14. An electrically conductive layer 18 is formed over metal pads 14 and passivation layer 16. Conductive layer 18 operates as a redistribution layer (RDL) to extend horizontal interconnect of metal pads 14. A passivation layer 20 is formed over conductive layer 18 and passivation layer 16. A portion of passivation layer 20 is removed by an etching process to expose conductive layer 18. Bumps 22 are formed over conductive layer 18 in the removed portions of passivation layer 20.
The contact interface between bumps 22 and RDL 18 are subject to rejection or failure, particularly during manufacturing reliability testing. Passivation layer 20 is intended to maintain the seal for the contact interface between bumps 22 and RDL 18. However, if passivation layer 20 delaminates from bumps 22, moisture can penetrate through the separation between the passivation material and bump and cause oxidation around the contact interface between bumps 22 and RDL 18. The oxidation weakens the contact interface. The device can be rejected by post-reliability inspection, or the device could fail in the field.